1. Field of the Invention
The present invention relates to a method of manufacturing a gate electrode in which a fine gate electrode can effectively be manufactured by thickening a resist opening for gate electrodes formed by ordinary electron beam lithography so as to reduce opening dimensions, to a gate electrode which is manufactured by the method of manufacturing a gate electrode and is used favorably for a field-effect transistor which has excellent high frequency properties and is useful for a transmitting and receiving device of quasi-millimeter and millimeter band waves or a high-speed signal processing (optical communication) device, and to a semiconductor device using the gate electrode and method of manufacturing thereof.
2. Description of the Related Art
Field-effect transistors having superior high frequency properties are useful as devices for transmission/reception of quasi-milliwave and milliwave band radio waves or as devices in high-speed signal processing (for optical communications). In the developments of the gate electrode used for the device, particularly in which excellent high frequency properties are required, there has been extensive effort on making the gate length as short as possible by forming opening for forming gate using electron beam lithography.
In the related art, to form micro-openings for gates by electron beam lithography, it was proposed to (1) make the electron beam used for patterning very fine so as to form a fine pattern, and (2) apply heat to the resist in which the opening for the gate electrode is formed, thereby softening it to reduce the opening dimensions.
However, there are the following problems in these cases. Specifically, in (1), although in the related art it was possible to make the electron beam diameter as fine as 0.04 μm, this technique was still inadequate from the viewpoint of stable manufacture when several thousands of transistors were assembled. In (2), because the amount of the reduction of the opening dimensions obtained stably is about 0.04 μm or less, reducing the opening dimensions drastically beyond this creates problems in the uniformity, and is not suited for mass-production. Further, it was inherently difficult to use the same opening to form both a recess opening and gate electrode opening which have a large dimensional difference.
Accordingly, an object of the present invention is to provide a method of manufacturing a gate electrode in which a fine gate electrode can effectively be manufactured by thickening a resist opening for gate electrodes formed by ordinary electron beam lithography so as to reduce opening dimensions. Another object of the present invention is to provide a gate electrode which is manufactured by the method of manufacturing a gate electrode and is used favorably for a field-effect transistor which has excellent high frequency properties and is useful for a transmitting and receiving device of quasi-millimeter and millimeter band waves or a high-speed signal processing (optical communication) device. Yet another object of the present invention is to provide a high-performance semiconductor device using the gate electrode, and a method of efficiently manufacturing thereof.